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Q1. Consider the following statements about a physical change. I. The shape or size of the substance may change. II. The state of the substance may change. III. A new substance with different properties is always formed. Which of the statements are correct?
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Q2. Assertion (A): Curdling of milk is a chemical change. Reason (R): In curdling, a new substance with different properties is formed and the change cannot be reversed.
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Q3. Asha says that boiling of water in an open pan is a chemical change because steam looks very different from water. Using the chapter's criterion, the best response is
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Q4. In Question 10 of the chapter, four experiments are set up: (a) Vinegar + baking soda → lime water, (b) Lemon juice + vinegar → lime water, (c) Vinegar + common salt → lime water, (d) Lemon juice + baking soda → lime water. In which case(s) will lime water turn milky?
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Q5. The chapter represents Activity 5.4 in short form as: Vinegar + Baking soda → ____ + Other substances. The missing product, which can be tested with lime water, is
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Q6. Nalini sees a brown deposit on the handle of her bicycle. Using the chapter's fill-in-the-blank framing, the brown deposit is due to ____ and this is a ____ change.
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Q7. Consider the burning of magnesium ribbon. I. A new substance — magnesium oxide — is formed. II. Heat and light are produced. III. It is a physical change because only the appearance of the ribbon changes. Which statements are correct?
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Q8. In Activity 5.6 a piece of paper catches fire when sunrays are focused on it with a magnifying glass, even without a flame. The best explanation according to the chapter is that
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Q9. The Science and Society box advises that if a person's clothes catch fire, the best response is to wrap a blanket or cloth around them. The chapter's reason is that this
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Q10. About the burning of a candle, three statements are made. I. The melting and solidification of wax are physical changes. II. The wax of the candle, carried up the wick, evaporates due to the heat of the flame. III. The vapour of wax burns and this is a chemical change. Which statements are correct?
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Q11. Assertion (A): Making popcorn from corn cannot be reversed. Reason (R): Once the corn kernel has popped, we cannot get the original corn kernel back.
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Q12. A change which is undesirable in one situation may be desirable in another. Which pair illustrates this most directly?
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Q13. Three statements compare weathering and erosion: I. Weathering breaks rocks into smaller pieces, while erosion moves the broken material from one place to another. II. Weathering can be both physical and chemical, while erosion by wind and flowing water is a physical change. III. Erosion eventually leads to the formation of soil. Which are correct?
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Q14. The chapter (Fig. 5.10b) shows a black rock called basalt, which contains iron, developing a red-coloured layer over a long time. The red colour is due to
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Q15. In Question 9 of the chapter a Venn diagram has region A for physical changes, region B for chemical changes, and overlap region C for changes that are both physical and chemical. Which of the following belongs in region C?
